列表的增、删、改、查

列表的增、删、改、查

l1 = ["a","b","c",1,2]
print(l1[-1:1:-1])  [2, 1, 'c']
#增
l1.append("summer") #增加到列表的最后位置

l1.insert(1,"aaaa") #根据索引添加元素

l1.extend([3,4,5,6]) #将序列里面的元素迭代的添加到列中
print(l1)  ['a', 'b', 'c', 1, 2, 3, 4, 5, 6]

l1.extend(["rain",["egon","23"]])
print(l1) ['a', 'b', 'c', 1, 2, 'rain', ['egon', '23']]

#删除
# res = l1.pop() #删除最后一个,有返回值
print(res)
# res = l1.pop(2) #按照索引删除，有返回值

# res = l1.remove("a") #按照元素删除，没有返回值

# l1.clear()  #清空数据

#del删除
#del l1[0]  #按照索引删除
# del l1[:2] #切片删除
#del l1  #将l1从内存中删除

#改
1、通过索引直接修改
l1[1] = "alex" 
2、通过切片修改或者添加
# l = ["a","b","c","d","e","f"]
# l[0] = [1,2,3] #直接将列表添加到索引位置处

# l[1] = {"name":"summer"}  
# print(l) ['a', {'name': 'summer'}, 'c', 'd', 'e', 'f']

# l[:2] = [1,2,3,4] #切片后将数据迭代的添加到被切除的位置
# print(l) [1, 2, 3, 4, 'c', 'd', 'e', 'f']

# l[0:1] = [9,8,7]
# print(l) [9, 8, 7, 'b', 'c', 'd', 'e', 'f']

# l[1] = ["summer","rain"]
# print(l)

# l[0:4:2] = [11,22] #切片加步长。切了多少个元素就要相应的添加多少个元素，否则直接报错
# print(l) [11, 'b', 22, 'd', 'e', 'f']


##排序
l1 = [1,3,4,23,76,21,54,56,12]
l1.sort()  #当列表里面的元素全部是由数字组成时，从小到大排序
print(l1) [1, 3, 4, 12, 21, 23, 54, 56, 76]

l1.sort(reverse=True)  #从大到小排序
print(l1)  [76, 56, 54, 23, 21, 12, 4, 3, 1]

l1.reverse()  #将列表里面的元素的顺序翻转
print(l1)  [12, 56, 54, 21, 76, 23, 4, 3, 1]
print(l1[::-1])  #切片反序  [12, 56, 54, 21, 76, 23, 4, 3, 1]